Attenuated strains of Salmonella have been used as carriers of heterologous antigens for human and animal vaccination. in mice, S. typhimurium normally infects macrophages in the Peyer's patches of the gut and also cells of the liver and the spleen. We will compare the immune response of mice orally- inoculated with S. typhimurium which expresses one of two model antigens: (l) Simian immunodeficiency virus gag protein (SIV gag) and (2) the B subunits of Shiga-like toxin type l (SLT-l) and SLT-ll from Enterohemorragic E. coli. One of these strains, designed to enhance a cellular immune response to an antigen, will deliver DNA encoding the IL-1 2 cytokine and the SIV gag protein directly to macrophages which will then appropriately transcribe, translate, and process these proteins. To do this, the Salmonella strain will contain two sets of prokaryotic genes under a tightly regulated promoter that after phagocytosis will 1) liberate the bacteria from the phagosome into the cytoplasm of a macrophage, and then 2) lyse the bacterium thereby releasing a prokaryotic/eukaryotic shuttle vector carrying cytokine and viral DNA into the cytoplasm of the macrophage. Those macrophages infected with the Salmonella carrier strains will process the antigen and co-express specific cytokines thus resulting in a targeted and specific enhanced immune response. One of the other strains, designed to augment a mucosal immunity, will co-express IL-5, a cytokine that augments slgA production, together with the SLT protective antigens. finally, we will use the Salmonella vaccine system to evaluate the type of T cell response generated to a heterologous antigen that is delivered via a vaccine strain directly to the cytoplasm of an antigen presenting cell. The results from these studies have direct application to the production of effective vaccines that can specifically modulate the immune system to develop a protective response against intracellular and extracellular pathogens.